Reactor for the production of lead oxide with a high free-lead content

ABSTRACT

A reactor for partially oxidizing molten lead with air to produce lead oxide with a high free-lead content includes a chamber, a variable speed rotatable stirrer positioned in the chamber, an air inlet venturi extending into the chamber and inclined from the vertical in the direction of rotation of the stirrer, a spout for introducing molten lead into the chamber, a deflector mounted upstream of the spout with respect to the direction of rotation of the stirrer, an exhaust duct for the lead oxide extending into the chamber, being substantially aligned with the vertical axis of the chamber and having adjustable holes communicating with the atmosphere, means for cooling the chamber and means for creating a sub-atmospheric pressure in the chamber.

llnite States Patet [1 1 lLeslbros et al.

[ Sept. 17, 1974 [75] Inventors: Andre Jose Lesbros; Max Jacques RaoulBrachet, both of Rieux, France [73] Assignee: Societe Miniere EtMetallurgique De Penarroya, Paris, France [22] Filed: June 7, 1972 [21]Appl. No.: 260,456

[30] Foreign Application Priority Data June 10,1971 France 71.21066 [56]References Cited UNITED STATES PATENTS Grapp 432/233 Hull et al. 432/233Vahrenkamp et al. 136/27 Primary ExaminerJames H. Tayman, Jr. Attorney,Agent, or Firm-Fleit, Gipple & Jacobson [5 7 ABSTRACT A reactor forpartially oxidizing molten lead with air to produce lead oxide with ahigh free-lead content includes a chamber, a variable speed rotatablestirrer positioned in the chamber, an air inlet venturi extending intothe chamber and inclined from the vertical in the direction of rotationof the stirrer, a spout for introducing molten lead into the chamber, adeflector mounted upstream of the spout with respect to the direction ofrotation of the stirrer, an exhaust duct for the lead oxide extendinginto the chamber, being substantially aligned with the vertical axis ofthe chamber and having adjustable holes communicating with theatmosphere, means for cooling the chamber and means for creating asub-atmospheric pressure in the chamber.

6 Claims, 2 Drawing Figures REACTOR FOR THE PRODUCTION OF LEAD OXIDEWITH A HIGH FREE-LEAD CONTENT It is well-known that litharge with a highfree lead content is generally produced by partial oxidation of liquidlead by the oxygen contained in the air. This oxidation takes place in areactor which comprises means for introducing air and molten lead intoit, together with a rotating stirrer which improves the contact betweenthe metal and the oxidizing agent. Such known reactors comprisefurthermore a heating chamber for initiating the reaction. An example ofthese reactors is the so-called Barton pot" is described for instance inthe French Pat. No. 400,270.

These known devices are subjected to various drawbacks among which thatit takes a long time to start the reactor, the difficulties which aremet when a control of the quality of the obtained product is wished,i.e., among others a control of its free lead content and of itsgranulometry, the frequent cleaning operations and the unsatisfactyingyield.

Consequently, one object of the present invention is to provide for areactor of the above-mentioned type which improves the contact betweenthe molten lead and the air which transforms the metal into lead oxide.

Another object is to obtain a faster and less expensive starting of suchreactors.

A further object is to provide for a reactor for producing lithargewhich allows an easy control of the quality of the obtained product and,notably, the production of litharge with a high proportion of free lead,i.e., litharge with to 35 weight-% free lead, this composition remainingconstant.

These objects and others which will appear further below are reached bythe reactor according to the invention which comprises in combination acircular chamber, a rotating stirrer in this chamber, means for rotatingsaid stirrer which are located under said stirrer means for adjustingthe rotation speed of said stirrer, a liquid lead inlet spout, an airinlet venturi protruding into the chamber and inclined from the verticalin the direction of the rotation of the stirrer, a double shelf orjacket arranged around the chamber and provided with means forcirculating in it cooling air in order to evacu ate from the chamber afraction of the heat produced by the oxidation of the lead, and anexhaust duct for evacuating from the chamber the produced oxide.

The stirrer is rotated by a shaft which passes through the lower part ofthe reactor and the duct for evacuating the produced oxide canconsequently be placed following the axis of the reactor.

These dispositions, on the one hand, improve the contact of the moltenlead with the air and, on the other hand, allow the device to operatelike a cyclone which provides for the size classification of theproduced lead oxide.

The starting of the installation is advantageously carried out, not byexternally heating the reaction chamber, but by means of burners locatedin the air inlet venturi, which shortens substantially the duration ofthe starting.

Feeding the reactor with molten lead is preferably carried out by meansof a constant-flow pump which works intermittently. Furthermore, theexhaust duct for evacuating the produced litharge may be provided withadjustable openings which control the quantity of air flowing throughthe inlet venturi.

The installation according to the invention may also comprise, on theone hand, a deflector mounted upstream of the liquid lead inlet spout inthe rotation direction of the stirrer its function will be precisedbelow and, on the other hand, means for cooling the bearing in whichsaid stirrer is mounted.

The following description has no limitative character and will allowthose skilled in the art to readily understand how the present inventioncan be carried out. It must be read with reference to the accompanyingdrawings among which:

FIG. 1 is a schematical view of the reactor in a vertical cross-section.

FIG. 2 shows the object of FIG. 1 in a partially cut horizontalcross-section.

The reactor according to the invention comprises a cylindrical chamber1, the bottom 2 of which is conically shaped and upwards flared. Astirrer 3 is provided for instance with three arms 4a, 4b and 4c andpresents the same shape as bottom 2 without contacting it. This stirrer3 is rotatably mounted around an axis extending downwardly and shownschematically at 5. The stirrer 3 is rotated in the direction of arrow 6by a device not shown of any classical type. It will be readilyunderstood that this disposition leads for the product to be treated tothe superposition of a radial movement on the circular stirring inducedby the stirrer 3 during its rotation. The rotation speed of the stirreris adjustable, which allows to control the intensity of the stirring andconsequently, the oxidation rate of the lead.

The cover 7 of chamber 1 is also conical, but downwardly flared. Throughthis cover passes an air inlet venturi 8, the geometrical axis 9 ofwhich is, according to the invention, inclined from the vertical in thedirection of the rotation of stirrer 3. More precisely, and in the caseof the device shown on the drawings, the angle of this axis 9 with thevertical is about 40 and its horizontal projection is tangent to acircle with its center on the axis of chamber l and a radius equal toabout 0,4 times the radius of this chamber. If one supposes it isoriented downwards, it is directed like arrow 6.

It will be easily understood that "the above-cited numerical values area function of the dimensions of the reactor and, more specifically, ofits height/diameter ratio. Those skilled in the art will determinereadily these numerical values in each particular case encountered,being given that the introduced air must be given a downwardly curlingmovement, in order to allow the apparatus to operate like a cyclone.This disposition permits, in fact, a mechanical sorting of the particlesinto sizes, as will be shown below.

Furthermore, the venturi 8 is arranged for removably placing into itburners which are shown very schematically at 10, for purposes givenbelow.

The molten lead to transform partially into litharge is introduced intochamber 1 by means of a spout l1 fed by a pump (not shown). The startingand stopping of this pump are controlled by a timer which is previouslyadjusted depending on the production of the apparatus and on the qualityof the oxide to be produced.

A deflector 12 is mounted in chamber 1 upstream of spout 11 with respectto the rotation direction of stirrer 3. It consists in a cylindricalvertical metal sheet with one vertical edge fixed along a generatrix 13of the lateral wall of chamber 1 and it extends inwardly till about 2/3of the radius from the center. The function of this member is mainly toavoid a solidification of the lead stream and an escape of air and dustthrough the inlet spout for liquid lead. Pyrometrical rods are mountedbetween deflector 12 and spout 11.

The litharge is produced by reaction of the air introduced throughventuri 8 with the lead entering into the reactor through spout 11. Thisoxide is evacuated through an axial pipe 15 passing through cover 7 ofchamber 1. In fact, this pipe 15 is connected to an exhaust fan (notshown) which maintains a subatmospheric pressure in the inside of thechamber. Furthermore, this pipe is provided with adjustable holes 16which allow, by a by-pass effect, the control of the quantity of airflowing into venturi 8.

On the other hand, an axial pipe 17 passes through pipe 15 for purposesgiven below. At its upper end, this pipe is connected to a horizontalpipe which passes through pipe 15 and opens in the external atmosphere.

The chamber 1 itself is mounted in a jacket 18 provided with an inlet 19and an outlet 20 for cooling air. in fact, it is well-known that theoxidation of lead is strongly exothermic, and this cooling air, whilecirculating in the space 21 between chamber 1 and jacket 18 evacuates afraction'of the heat released by the reactron.

Lastly, a cone 22 passes through the lower part of jacket 18. This conesupports the bearing (not shown) in which the shaft of stirrer 3rotates. This bearing is cooled by air pulsed into cone 22 by means of afan (not shown) and, at its upper end, by means of the pressure drop inchamber 1. (see below).

This device is operated as follows: the installation is first preheatedby means of burners l0 removably mounted in the air admission venturi 8.This preheating takes place till a temperature is reached which is atleast equal to the smelting point of lead. Molten lead is thenintroduced into chamber 1 through spout l1 and the metal is oxidised byair with a strong release of heat which increases the temperature in thechamber. As soon as an optimum value is reached, it is maintainedconstant by adjusting the holes 16 which control the flow of air throughventuri 8 and/or by adjusting the flow of cooling air through the space21 provided between chamber 1 and jacket 18. Due to the fact that thereactor works like a cyclone, as mentioned before, the particles whichare fine enough escape through pipe 15, and the other ones come intocontact with the wall of the chamber and fall towards the bottom 2 wherethey are worked again by agitator 3. At the outlet of the pipe 15, finelead oxide with a very homogeneous granulometry is obtained.

The air flowing through pipe 17 due to the subatmospheric pressure inchamber 1 cools the bearing in which the shaft of stirrer 3 is mounted.

The proportion of free lead in the produced oxide is obviously afunction of the rotation speed of stirrer 3, of the lead feed-rate intothe apparatus and of the temperature within chamber 1. By means ofseveral preliminary tests, those skilled in the art will readilydetermine the values to be chosen for these parameters in eachparticular case.

What I claim is:

1. A reactor for partially oxidizing molten lead with air to producelead oxide with a high free-lead content, comprising in combination acylindrical chamber, a rotatable stirrer positioned in said chamber,means for rotating said stirrer at a variable speed, said rotating meansbeing located under said stirrer, an air inlet venturi extending intosaid chamber and inclined from the vertical in the direction of rotationof said stirrer, a spout for introducing molten lead into said chamberex tending into said chamber and connected with a pump fed with moltenlead, a deflector mounted upstream of said spout with respect to thedirection of rotation of said stirrer, an exhaust duct for said leadoxide extending into said chamber, said exhaust duct being substantiallyaligned with the vertical axis of said chamber, and having adjustableholes communicating with the atmosphere, means for cooling said chamber,and means for creating a subatmospheric pressure in said chamber.

2. The reactor according to claim 1, wherein said stirrer has threearms.

3. The reactor according to claim 1, and further comprising burnersremovably mounted on said air inlet venturi for heating the air.

4. The reactor according to claim 1, wherein said stirrer is mounted ina bearing which is in contact with the atmosphere at its lower end andwherein said reactor further comprises means for cooling the upper endof said bearing.

5. The reactor as claimed in claim 4, wherein said means for cooling theupper end of said bearing comprises a vertical tube coaxial with saidexhaust duct and located within said duct, said vertical tubecommunieating with the atmosphere.

6. The reactor as claimed in claim 1, wherein said means for creating asub-atmospheric pressure comprises a suction fan connected to saidexhaust duct.

2. The reactor according to claim 1, wherein said stirrer has threearms.
 3. The reactor according to claim 1, and further comprisingburners removably mounted on said air inlet venturi for heating the air.4. The reactor according to claim 1, wherein said stirrer is mounted ina bearing which is in contact with the atmosphere at its lower end andwherein said reactor further comprises means for cooling the upper endof said bearing.
 5. The reactor as claimed in claim 4, wherein saidmeans for cooling the upper end of said bearing comprises a verticaltube coaxial with said exhaust duct and located within said duct, saidvertical tube communicating with the atmosphere.
 6. The reactor asclaimed in claim 1, wherein said means for creating a sub-atmosphericpressure comprises a suction fan connected to said exhaust duct.